Gas turbines can typically be operated only in a restricted way in their power range toward the lower partial load ranges because of limit value requirements for the CO emission quantities. This is because, when the partial load operation is reduced to lower powers, the primary zone temperature of the combustion typically decreases continuously. When this primary zone temperature falls below a temperature limit value typical of a gas turbine, the amount of CO emission increases, sometimes exponentially, since the combustion of CO to form CO2 can no longer take place to a sufficient extent. When predetermined limit values are reached, the partial load operation must therefore be restricted to lower powers in order not to violate the CO emission limit values. Such a restriction likewise has an effect on the operation of a steam turbine system coupled to such a gas turbine (in the sense of a Combined Cycle Power Plant, CCPP), since a power reduction possibly desired by the operator is not to be reached below a limit value.
Because of compliance with predetermined CO emission limit values, a power plant operator is thus obliged to periodically turn off the gas turbine, or a steam power plant system coupled to this gas turbine, or remain in a partial load range which lies above the technically possible minimum power.
There is consequently a technical requirement to provide a gas turbine, or a method for operating such a gas turbine, making it possible to reduce the partial load range further without simultaneously exceeding CO emission limit values. In other words, the partial load range of the gas turbine is intended in particular to be extended downward while complying with CO emission limit values. Above all, this partial load range should be provided below the otherwise technically available load range which can be achieved by suitable guide vane adjustment (so-called guide vane adjustment range).
One solution approach for these technical requirements may be specified by the publications US 2010/0175387 A1 and U.S. Pat. No. 5,537,864. In these documents, it is proposed to adjust the amount of air blown out from the compressor by suitable control by means of a bypass flow channel, in such a way that the primary zone temperature does not change substantially. Since the primary zone temperature itself cannot be measured directly, however, these controls always rely on predetermined assumptions, or estimates.
At this point, it should be pointed out that the primary zone temperature (TPZ) is an average temperature determined from the energy balance around the burner and flame, which describes the thermodynamic state of the hot gas after completed chemical reaction. The TPZ therefore correlates with the proportion of CO in the combustion gases.
It is therefore desirable to provide a more highly developed method which can avoid the above-mentioned problems of the prior art, and at the same time can provide reference quantities that can be metrologically recorded better.